I fell in love with the name Contessa as a child after watching the movie Ever After when Drew Barrymore's character introduces herself to PrinceHenry as "CountessNicole de Lancre". It sounded so beautiful coming out of her mouth. It wasn't until years later that I realized what I thought was her first name was a title, haha. I still think Contessa is beautiful, especially as a route for nn Tess, but maybe not so usable anymore. It was on my list for a while, though!

I love the Esther & Quintessa suggestions! At first read, I thought the sound was nice despite the fancy title aspect, but after giving it more thought the Cont beginning is problematic for me as it could result in vulgar teasing.

I think you could get to Tess with a name like T____ Agnes as well, a kind of smoosh nickname that opens up your options.

Thais is lovely. I say Tah-ees, not far from a softer Therese and not far from a more romantic Tess.